How can I send data back to the first view controller after detecting that the back button was pressed?

Question

Now Using the Delegate Pattern to transfer the data:

I have implemented this function:

 var overviewController = addOverview()

override func viewDidLoad() {
    super.viewDidLoad()
    // Do any additional setup after loading the view.
    overviewController.delegate = self
}

func setValues(){
    overview.name = buildingName.text!
    overview.city = city.text!
    overview.contact = contactName.text!
    let dateFormatter = DateFormatter()
    dateFormatter.dateFormat = "MM-dd-yyyy"
    overview.date = dateFormatter.string(from: datePicker.date)
    overview.email = email.text!
    overview.building = buildingTypes[buildingPicker.selectedRow(inComponent: 0)]
    overview.freq = cleaningFreqs[cleaningFreqPicker.selectedRow(inComponent: 0)]
    overview.phone = phoneNumber.text!
    overview.sft = sqFt.text!
    overview.state = State.text!
    overview.street = street.text!
}



// MARK: - Navigation

override func willMove(toParent parent: UIViewController?) {
    super.willMove(toParent:parent)
    if parent == nil {
        setValues()
        print("Hello")
        delegate?.setValues(obj: overview)
    }
}

And here i the setValues from the protocol I wrote:

func setValues(obj: overviewProps){
    overview = obj
}

However after printing one of the properties of the object, the data has not been transferred.

Answer 1

There are many ways to pass/exchange data between two viewControllers. I do not know how your implementation look like. But you can use delegate pattern to achieve your target. Use a delegate and trigger the methods when you want to pass data.

As I said there are other solutions, too. But it is up to you, which one you want to choose.

Answer 2

You can use Delegate pattern or use Observer. See these examples for help.

• Delegate: https://www.appcoda.com/swift-delegate/
• Observer: NSNotificationCenter addObserver in Swift

Edit: using delegate based on your code

Protocol

protocol SetValueDelegate {
    func didFinishSetValue(obj: Overview)
}

First view controller

class FirstViewController: UIViewController, SetValueDelegate {

   var secondViewController = SecondViewContrller()

   override func viewDidLoad() {
       super.viewDidLoad()
       secondViewController?.delegate = self
   }

   func didFinishSetValue(obj: Overview) {
       // when it comes back to the first screen you can use ->> obj data
   }

}

Second view controller

class SecondViewController: UIViewController {
   var delegate: SetValueDelegate?

   override func viewDidLoad() {
       super.viewDidLoad()
       …
   }
   override func willMove(toParent parent: UIViewController?) {
      super.willMove(toParent: parent)
      if parent == nil {
         setValues()
         …
         self.delegate?.didFinishSetValue(obj: overview)
      }
   }

}

Answer 3

The proper way to pass data between the current view and the root view with your navigation design is to trigger an unwind segue.

Have a look at the follow article. It is in Swift 3, but it should give you a good start in translating that into Swift 4.2

https://link.medium.com/b4eFIx7LaV